<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div{
            width: 300px;
            height: 200px;

            border-width: 5px;
            border-style: solid;
            border-color: red;
            /* 边框的复合写法 ，没有顺序*/
            /* border: red 1px solid; */

            /* 上边框*/
            /* border-top: 5px solid rebeccapurple; */
            /* 下边框 */
            /* border-bottom: 5px solid green; */


            /* 上边框为红色，其余为蓝色 */
            border: 1px solid blue;
            /* 层叠性 */
            border-top: 1px solid red;
        }
    </style>
</head>
<body>
    <div></div>
</body>
</html>